Variation in FDG Uptake on PET in Patients with Radiation-induced Pelvic Insufficiency Fractures: a Review of 10 Cases

Introduction: The information available on (18)F-fluorodeoxyglucose (FDG) uptake on PET in radiation-induced pelvic insufficiency fracture (PIF) is limited. In this study, we reviewed the findings of FDG-PET in 10 cases with PIF.

Materials And Methods: We diagnosed 83 cases of PIF in patients who received pelvic radiotherapy between Jan 1995 and Aug 2005. Among these patients, we selected 10 patients who performed FDG-PET and reviewed the FDG uptake.

Results: Mild FDG uptake was still present at 6-months after the diagnosis of PIF in two patients. Eight patients had mild and diffuse FDG uptake and two patients had intense and heterogeneous uptake. All patients had vertical uptake parallel to the sacroiliac joints and one patient had the typical 'H' sign associated with PIF. The maximum of standardized uptake values was variable and ranged from 2.4 to 7.2. In three patients, follow-up PET images were obtained. All patients had FDG uptake that decreased with time.

Conclusion: The FDG-PET demonstrated a variable degree of uptake in patients with a PIF. The pattern of uptake was diffuse and vertical, parallel to the sacroiliac joints. Therefore, clinicians should be careful with the interpretation of FDG uptake around the sacroiliac joints, and keep in mind false-positive lesions such as PIFs.